Fentanyl

What it is (core concept)

• Fentanyl is a strong opioid (µ-opioid receptor agonist) used for analgesia and to reduce the stress response to surgery and airway instrumentation.
• Very potent: roughly 100 times as potent as morphine (so doses are in micrograms, not milligrams).
• Highly lipid soluble → fast onset after IV dosing; can accumulate with repeated doses/infusions (context-sensitive half-time increases).

Common uses in anaesthesia (first-time scenarios)

• Induction: reduce response to laryngoscopy/intubation and provide early analgesia.
• Intra-op analgesia: boluses or infusion as part of balanced anaesthesia (often alongside volatile/TIVA).
• Procedural sedation/analgesia: only with appropriate monitoring and airway skills immediately available (risk of apnoea).
• Post-op pain: less common as a standalone ward analgesic; more often in theatre/recovery or via PCA/infusion in selected settings.

Dosing (practical starting points — always individualise)

• Typical IV bolus for induction/analgesia: 0.5–2 micrograms/kg (often given in small increments).
• Blunting intubation response: commonly 1–3 micrograms/kg IV given a few minutes before laryngoscopy (balance against hypotension/apnoea).
• Incremental top-ups intra-op: e.g., 25–50 micrograms IV at a time, titrated to clinical signs and surgical stimulus.
• Reduced doses in: older/frail patients, hypovolaemia, significant cardiorespiratory disease, and when combined with other sedatives (propofol, benzodiazepines).

Onset, duration, and what you’ll see

• IV onset: usually within 1–2 minutes; peak effect often around 3–5 minutes (plan timing before stimulation).
• Single bolus duration: around 30–60 minutes for analgesic effect, but respiratory depression may outlast perceived analgesia.
• Expected effects: analgesia, reduced sympathetic response (lower HR/BP), sedation, respiratory depression, cough suppression.

Side effects (what to anticipate and manage)

• Respiratory depression/apnoea: dose-related; risk increases with other sedatives and in opioid-naïve patients.
• Bradycardia and hypotension: more likely with higher doses, vagal stimulus, or co-induction agents.
• Chest wall rigidity (rare but important): can make ventilation difficult, usually with rapid/high-dose IV administration; treat with neuromuscular blockade and ventilation support.
• Nausea/vomiting, pruritus, urinary retention: typical opioid effects (often more relevant post-op).
• Reduced gut motility/constipation: consider in post-op prescribing.

Monitoring and safety essentials

• Always use appropriate monitoring: ECG, NIBP, SpO2; capnography is essential whenever ventilation may be affected (including sedation).
• Give in small, titrated increments; allow time to see peak effect before re-dosing.
• Be ready to support airway/ventilation: oxygen, bag-mask ventilation, airway adjuncts, and escalation plan.
• Document dose (micrograms), time, and response; communicate total opioid given to recovery staff.

Preparation and administration (avoiding errors)

• Common concentration: 50 micrograms/mL (check local presentation; some areas have different strengths).
• Label syringes clearly and keep opioids separate from induction agents to reduce swap errors.
• State dose in micrograms and micrograms/kg; avoid ambiguous shorthand (e.g., avoid writing just “fentanyl 2”).
• Give slowly in most routine cases; rapid bolus increases risk of apnoea and rigidity.

Reversal and rescue (naloxone basics)

• Naloxone reverses opioid effects (including respiratory depression).
• Use small, titrated doses to restore adequate ventilation while avoiding severe pain, agitation, hypertension, or acute withdrawal in opioid-tolerant patients.
• Naloxone duration may be shorter than fentanyl effect → monitor for re-sedation and consider repeat dosing/infusion as per local guidance.

Special situations (intro level)

• Elderly/frail: start low, go slow; increased sensitivity and higher risk of hypotension and respiratory depression.
• Obesity/OSA: higher risk of airway obstruction and post-op respiratory events; careful titration and enhanced monitoring in recovery.
• Renal impairment: fentanyl is generally less affected than morphine by active metabolite accumulation, but clinical effect still varies—titrate to effect.
• Haemodynamic instability: fentanyl can be useful (minimal histamine release), but high doses can still cause bradycardia and hypotension.